Warm the tortillas using the package directions. Cut the onion into halves through the stem end. Slice into half-rings. Melt the butter in a large skillet over medium-high heat. Add the onion and bell peppers. Cook for 6 to 8 min. or until the onion is golden brown, stirring occ. Remove from the heat. Add the garlic salt, cheese and roast beef and mix well.

Spoon 1 c. of the mixture onto the center of each tortilla. Fold 1 edge of the tortilla over the filling toward the center. Roll to enclose the filling. Place 2 wraps seam side down on a microwave-save plate. Mocrowave on high for 1 to 2 min. or until heated through, turning the plate halfway through the cooking time. Repeat with the remaining wraps